Question

15 stamps of equal value cost $18.00. what will be cost of 22 such stamps.

Answer 1

First of all, let's find out the value of 1 stamp

15 stamp = $18

1 stamp = 18/15 = $1.2

Now the value  of 22 such stamps 

22*1.2 = $26.4

Answer 2

Let the cost of 1 stamp be ........$X
ATQ.....
15*X=$18.00
X=18/15
X=1.2


Then,
Cost of 22 stams is..........$1.2*22
=$26.4